This application relates to a resistance welding electrode for welding fasteners to a metallic object, for example. More particularly, the application relates to an insulating sleeve used to insulate a pin from an electrode head.
Weld gun assemblies are used to resistance weld fasteners to metallic objects, such as body panels for vehicles. A fastener such as a weld stud or nut is loaded onto one of the electrodes. The electrodes are moved together with an actuator placing the fastener into engagement with the panel under pressure. Very high currents are applied to the electrodes, which welds the fastener to the panel. The use of weld guns is typically an automated process in which the fasteners are loaded into the weld gun assembly.
A widely used electrode in the industry utilizes a pin that receives a weld nut. The pin is biased to an extended position to receive the weld nut. The pin must be insulated from the electrode to prevent arcing. Further, the pin must move precisely to ensure that the nut is loaded properly on the pin. If arcing occurs, the surface of the pin could be damaged and prevent the unrestricted travel of the pin. Furthermore, a portion of the welding current will flow through the pin instead of the intended path through the nut and panel and the threads of the nut might be welded to the pin. Some pin arrangements are susceptible to debris, such as molten metal, becoming caught in the gap between the pin and head.
In one type of electrode, a stainless steel sleeve is arranged in an aperture in the electrode head through which the pin extends. A layer of fiberglass insulation bonds the stainless steel sleeve to the head and insulates the pin. Typically, both the stainless steel sleeve and head include grooves so the fiberglass interlocks the sleeve to the head. This type of insulating arrangement is more costly than desired.
Another example electrode includes a non-conductive ceramic coated pin. These pins are more costly to produce and are more difficult to precisely locate relative to the electrode head during welding operations. Another type of arrangement uses phenolic sleeves, which are adhered to the head. However, the phenolic sleeves are prone to swelling and mechanical deformation, which can permit undesired movement of the pin.
The prior art insulating sleeves extend the length of the aperture. The sleeve is typically chamfered after the outer face of the head, which supports the work piece, has been machined. Occasionally, molten metal produced during the welding process can become lodged in the chamfer thereby interfering with movement of the pin. Further, resurfacing the outer face after it has become worn requires the insulating sleeve to be chamfered again.
What is needed is a cost effective resistance welding electrode that provides precise pin location and is less susceptible to jamming from debris.